Chrome plating and anodizing stopoff composition



2,999,771 CHROW PLATING AND AN ODIZING STOPOFF COMPOSITION Norman I.Gaynes, 1254 Hedin Place, Rahway, NJ. No Drawing. Filed Apr. 17, 1958,Ser. No. 729,079 10 Claims. (Cl. 117- 132) This invention relates toimproved acid resistant coating compositions and more particularly to animproved form of coating composition suitable for producing anonconductive masking or stopotf coating which is highly resistant tostrong and highly oxidizing acid baths of the type used in chromiumplating as well as of the type used in anodizing.

Chromium plating is normally performed in strong chromic acid bathsutilizing small amounts of sulphuric acid. More recently, plating bathshave been developed which are self regulating and which permit highspeed plating, but even these contain highly oxidizing acidconcentrations which will attack and decompose many ordinary types ofcoatings.

Chromium metal, because of its hardness and ease of lubrication hasfound extensive use in rebuilding worn tools and dies by electrolyticdeposition. Where such tools and dies are to be electrolytically builtup with thicknesses of what is commonly known as hard chrome, eitherwith or without a base layer of nickel, it is usually desirable to applya coating to mask or stop oflf those areas exposed to the electrolyticbath'on which no plating is desired. Such coatings must have propertiessuflicient to withstand the severe corrosive conditions for long periodsof time. According to Faradays law, the amount of metal deposited at thecathode is a function of the current and the time. Thus, to deposit anappreciable amount of chromium metal, as in rebuilding of worn tools anddies, extended periods, up to as long as 48 hours or more, may berequired for the plating operation. A satisfactory stop off coating forchrome plating use must not only withstand this action of the strongoxidizing acids but also the erosion effect of hydrogen bubbling at thecathode for such extended periods.

Numerous acid-resistant coating compositions have been developed, but agreat disadvantage of many of these previous coatings is that they areefiective in chrome plating baths only for limited periods. Furthermore,many of the coatings produced from such compositions tend to be porousin some areas, and do not completely prevent penetration of the acidbath. Another common disadvantage is their extreme brittleness which isdeveloped under the highly acid conditions of a chrome plating bath.This brittleness often results in flaking off of the coating under theaction of hydrogen bubbling at the cathode.

In coatings for use inanodizing baths, as in chrome plating baths,similar problems have been experienced in connection with previous typesof stopoif coatings. Certain metals, such as aluminum .and magnesium,are anodized to protect their surfaces against corrosion and wear. Inthe anodizing process the metal parts to be anodized are placed at theanode and their surface is electrolytically coated with a hard porousamorphous oxide film to give it increased corrosion resistance anddurability. Generally the same types of acids as in chrome plating areused, for example chromic and sulphuric. However, many other acids suchas boric and oxalic acids have also been employed. With any of thesetypes of acids, whenever selective areas are to be anodized, a stop offor masking coating must be utilized which will withstand the corrosiveaction of the acids in the bath.

Another type of process in which masking or stopoii coatings findextensive application is in chemical milling or preferential etching. Ithas recently been found that such chemical milling or preferentialetching is far less expensive and as accurate as equivalent operationsperformed on milling machines or grinders. The properties required of asatisfactory stopofl coating composition are similar to those forprotection in electrolytic plating, and include ease of application,rapid curing, resistance of the film to attack by the chemical bath,adherence to the surface, and ease of removal.

it is therefore an object of the present invention to provide an organiccoating composition which can be cured at room temperature afterapplication by known painting methods, such as spraying, dipping,rolling, brushing, tumbling, etc. which will form a coating resistant tothe action of plating bath acids such as chromic and sulphuric, to theaction of anodizing baths, and to chemicals used in chemical milling andetching.

Another object of the invention is to provide a method facilitatingselective electroplating onto predetermined areas of a surface byproviding a stopoff coating film over the portions of the surface whichare to remain unplated.

Still another object of this invention is to provide a stabilizedcoating composition which will withstand lengthy storage in the liquidstate without deterioration of the coating composition and without lossof acid-resistant properties in the coatings produced therefrom.

A further object of this invention is the provision of a coatingcomposition which will form an adhering coating readily strippable bycontact with active ketone solvents or with vapor degreasers such astrichlorethylene, perchlorethylene, methylene chloride, and the like.

Still another object of this invention is to provide a coatingcomposition which will form a coating highly resistant to the erosioneffect of hydrogen developed at the cathode during electroplatingprocesses.

Another object of this invention is to provide a compo sition which canform a non-conductive coating which will impede the flow 10f ions ontoselected portions of a metal surface to be immersed in an electroplatingbath, thus preventing the molecular formation or metal deposition on thecoated areas.

Another object of this invention is to provide a coating compositionwhich can be dried at room temperature to develop full chemicalresistances, and can also be force dried to volatilize the solventstherein with an equality resistant film being formed by either dryingmethod.

A further object of the invention is to provide a nonconductive andnon-porous stopoff coating composition impervious to anodizing baths forselectively anodizing or forming an oxide filrn on predetermined areasof a surface of anodizable metals, such as aluminum and mag.- nesium.

A still further object of this invention is to provide a non-porousacid-resistant stopoif coating for protection of predetermined areas ofmetals in selective etching and chemical milling processes.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description.

These objects are accomplished by adding to a vinyl resin compositioncontaining at least in part a vinyl halide resin, a vinylchloride-acetate copolymer modified with about 1% interpolymerizedmaleic acid, a chlorinated biphenyl plasticizer, and propylene oxide asa stabilizer. A suitable solvent or diluent is added to produce thedesired viscosity, and an inert extender pigment may be added to providefilm homogeneity and to reduce porosity.

The higher molecular vinyl chloride-acetate copolymers are commerciallyavailable film forming vehicle constituents which form coatingsproviding excellent chemical resistance to most inorganic mineral acids.However, these resins cannot be used alone to form satisfactoryprotective coatings because of their inadequate;

adhesion qualities, brittleness and tendency to flaking. Consequently,other ingredients are necessary. Vinyl chloride-acetate copolymerssupplied under the trade name of VYNS by Bakelite Corporation, andcertain of the Exon resins supplied by Firestone Tire and Rubber Companyhave been found to be suitable for use as ingredients in the inventivecompositions described herein.

In order to improve the adhesion characteristics, according to theinvention, a vinyl chloride-acetate copolymer is added which has beenmodified with about 1% interpolymerized maleic acid. By way of example,the copolymer commercially available under the trade designation of VMCHas supplied by Bakelite Corporation, and Exon 470 as supplied by Fiestone Tire and Rubber Company, may be used in these inventivecompositions as the vinyl chloride-acetate copolymer modified withinterpolymerized maleic acid. The presence of carboxyl groupings of themaleic acid accounts for the improved adhesion, but the chemicalresistances tend to become somewhat diminished. Theref re, it ispreferable to include both types of vinyl chlorideacetate copolymers tobalance the chemical resistance of the first type with the adhesivecharacteristics of the second type. Too much of, either component in thecomposition will result in either lack of adhesion or lack of adequatechemical resistance.

A chlorinated biphenyl, preferably of the 60% chlorinated plasticizertype, such as, for example, that supplied under the trade name Arochlor1260 by Monsanto Chemical Company, is added to the composition toaccomplish a threefold purpose: Firstit increases the chemicalresistance of the coating; Second-it provides enough flexibility to thecoating to overcome the previously described tendency of the vinylchloride resin to brittleness and flaking; and Third-it improves thesolvent release of the vinyl copolymers. An excess of plasticizer,however, will tend. to keep the film open and thus porous.

The inventive composition material may be manufactured to produce aclear coating, but for greater ease of visibility during and afterapplication on a surface, opaque pigments, either white or colored, arepreferably added.

In order to provide greater homogeneity to the film and to producegreater resistance to the erosion effect of hydrogen bubbling, to reducetendency of the film to porosity and moisture penetration and toincrease the speed of dry, I prefer to add to the composition one ormore inert extender pigments, such as, for example, magnesium silicate,calcium silicate and the like. As an example of such an extender,magnesium silicate, or SF 399 Talc, supplied by Whittaker, Clark &Daniels has been used with success. Micronized talc such as SierraMistron may be substituted for the SF 399 Talc.

As a stabilizer to improve the packaged stability of the composition,according to the invention, I prefer to add propylene oxide. I havefound that this compound stabilizes the inventive composition so that itcan be stored for indefinitely long periods of time withoutdeterioration or decrease in chemical resistances of the coatings formedtherefrom.

The composition will contain, in addition to a resin of vinyl chloridetype, a vinyl chloride-acetate copolymer modified with interpolymerizedmaleic acid, a chlorinated biphenyl plasticizer, and propylene oxide, asuitable solvent or solvent mixture whereby the essential ingredientswill be blended and a solution or mixture formed of viscosity orfluidity such as to enable its application to a surface to be coated, asby brushing, spraying, dipping, or otherwise. The solvent or solventmixture will desirably be of a volatile nature and will act as avehicle, being Wholly or largely dissipated by, for example, evaporationafter application of the composition to a surface for the formation of afilm. The solvent may be of any suitable type for the purpose, as forexample, a mixture of methyl ethyl ketone, methyl isobutyl ketone andtoluol. Xylol may be substituted for toluol but will appreciably slowthe drying time and may cause tail end precipitation or haze. Thesolvent will desirably be a solvent for other ingredients which may beincluded in the composition, and will be used in an amount with relationto the ingredients to be dissolved such as to give the viscosity orfluidity desired.

In addition to the essential ingredients, vinyl chlorideacetatecopolymer, vinyl chloride-acetate copolymer modified withinterpolymerized maleic acid, chlorinated biphenyl, an extender andstabilizer, the composition, as has been indicated, may also containvarious other ingredients, as for example, pigments, etc. etc.Ingredients which may be included in the composition, in addition tothose indicated as essential may be included in varying amount as may bedictated by the characteristics of the additional ingredients and thepurpose for which the given composition is intended.

The proportions found most suitable are hereinafter set forth in Table Ias an illustrative example contemplated by the instant invention, thepercentages being by weight.

TABLE I Percent Vinyl chlonide-acetate copolymer 3.84 Vinylchloride-acetate copolymer modified with about 1% interpolymerizedmaleic acid 9.94 Chlorinated biphenyl 3.84 Methyl ethyl ketone 19.20Methyl isobutyl ketone 33.60 Toluol 14.92 Pigment 8.15 Extender(magnesium silicate talc) 6.40 Propylene oxide 0.11

It is to be understood that the proportions given in the above exampleare preferred, but that the proportions may be varied considerably, withand without ingredients other than those indicated herein as essential.Suitable proportions are from about 1.5% to about 6.3% vinylchloride-acetate copolymer, about 6.3% to about 15.5% of the copolymermodified with interpolymerized maleic acid, about 2.0% to about 6.0%chlorinated biphenyl, about 10.0% to about 30.0% methyl ethyl ketone,about 10.0% to about 60.0% methyl isobutyl ketone, about 5.0% to about20.0% toluol, about 2.0% to about 20.0% pigment, about 2.0% to about14.0% extender, and about 0.05% to about 1.5 propylene oxide.

Considering only the essential ingredients and taking the proportionatecontent of the unmodified vinyl chloride-acetate copolymer (for exampleVYNS) as unity, suitable proportions of non-volatiles present in thecornposition in relation thereto may be varied approximately as followswith satisfactory results:

TABLE II Ratio Vinyl chloride-acetate copolymer (VYNS) 1 Vinylchloride-acetate copolymer modified with about 1% interpolymerizedmaleic acid (VMCH) l.5-4.0 Chlorinated biphenyl (Arochlor i260) 0.5-2.5Extender (magnesium silicate) 0.5-4.5 Stabilizer (propylene oxide)0.01-0.9

Solvents, as required.

imately 150 F. for one hour, or instead may be airdried at roomtemperature overnight. A stopolf coating of sufficient thicknessprepared in this manner will resist the action of an acid plating bathor anodizing bath for 48 hours or more. After the plating operation iscompleted, the stopofi coating is removed by common active ketonesolvents. Vapor degreasers such as trichlorethylene, perchlorethylene,methylene chloride, and the like may be effectively utilized in additionto the ketone solvents in the removal operation.

As further examples of satisfactory compositions within the scope of thepresent invention, the following are disclosed, in addition to Example Ilisted in Table 1:

Exam le II I Approxim e Chemical desig- Compo Trade name Supplier nationsition by weight, percent Exon 450... Firestone Vinyl chloride 4.00

copolymer. Exon 470- dn dn 9. 78 Arochlor 1260 Monsanto Chlorinated 3.84

biphenyl. Methyl ethyl Shell Chemical 20 ketone. Methyl isobutyl do 33.60

ketone 8.15 Whittaker, Clark 6.40

& Daniels. Propylene oxide.- Union Carbide 0.11

Example III Approximate Chemical desig- Ccmpo- Trade name Suppliernation sition by weight% 6130811 p VYNS Bakelite Vinyl chloride- 5. 00

acetate copolymer. Exon 470 Firestone Vinyl chloride 7.50

copolymer. Arochlor 1260 Monsanto Chlorinated 3. 50

biphenyl. Arochlor 5460 do do 1. 62 Methyl ethyl Shell Chemical 19. 20

ketone. Methyl isobutyl do 33. 60

ketone. ToluoL 14.92 Pigment 8.15 SF 399 tale Whittaker, Clark Magnesiumsili- 6.40 & Daniels. e. Propylene oxide.. Union Carbide 0.11

Chemical.

While I have described a specific application of the 65 presentinvention, obviously many modifications and variations thereof arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

I claim:

1. An organic solvent solution of a vinyl chloride water immiscibleresin coating composition capable of drying at room temperaturecharacterized by its ability to deposit a film showing marked resistanceto acid chemi- 2. An organic solvent solution of a vinyl chloride waterimmiscible resin coating composition capable of drying at roomtemperature characterized by its ability to deposit a film showingmarked resistance to acid chemical attack and abrasion and showing ahigh degree of adhesion to the surface covered thereby, said compositioncomprising, by weight, about 150 to about 400 parts vinyl chloridemodified with about 1% interpolymerized maleic acid, about 50 to about250 parts chlorinated biphenyl of 60% chlorination, about 50 to about450 parts of a silicate extender, about 1 part to about parts propyleneoxide, about parts of an unmodified vinyl chloride-vinyl acetatecopolymer and a volatile vehicle.

3. A coating composition according to claim 2 and including an opaquepigment in an amount suhicient to impart opaqueness to a film producedfrom said composition.

4. An organic solvent solution of a water immiscible plating andanodizing stopolf coating composition capable of drying at roomtemperature comprising as principal film forming constituents anunmodified vinyl chloridevinyl acetate copolymer and a vinylchloride-vinyl acetate copolymer modified with maleic acid andcontaining as a plasticizer a chlorinated biphenyl of 60% chlorinationin an amount, by weight, from about 2.0% to about 6.0%, and includingabout 0.5% to about 1.5% propylene oxide, about 2.0% to about 14.0% of asilicate type extender, about 2.0% to about 20.0% of an opaque pigment,and a volatile vehicle.

5. A coating composition according to claim 4, Wherein said unmodifiedvinyl chloride-vinyl acetate copolymer is present in an amount, byweight, from about 1.5% to' about 6.3% and said copolymer modified withmaleic acid is present in an amount from about 6.3% to about 15.5%.

6. A coating composition according to claim 5, said volatile vehicleconsisting essentially of about 10% to about 30%, by weight, of methylethyl ketone, about 10% to about 60% methyl isobutyl ketone, and about5% to about 20% toluol.

7. An organic solvent solution of a non-aqueous stopoif composition forforming a stopoif masking fihn on selected portions of surface to beexposed to acids; said composition being capable of drying at roomtemperature and consisting substantially, by weight, of about 3.84%unmodified vinyl chloride-vinyl acetate copolymer, about 9.94% vinylchloride-vinyl acetate copolymer modified with about 1% interpolymerizedmaleic acid, about 3.84% chlorinated biphenyl of 60% chlorination, about19.2% methyl ethyl ketone, about 33.6% methyl isobutyl ketone, about14.92% toluol, about 8.15% of an opaque pigment, about 6.40% magnesiumsilicate talc, and about 0.11% propylene oxide.

8. A method of masking and impeding the flow of ions onto and fromselected portions of surfaces immersed in acid electroplating baths,anodizing baths, chemical etching baths and chemical milling baths,which comprises the steps of applying a plurality of coats of an organicsolvent solution of a non-aqueous composition comprised of a majorportion, by weight, of a blend of an unmodified vinyl chloride-vinylacetate copolymer and vinyl chloride-vinyl acetate copolymer modifiedwith interpolymerized maleic acid, and minor portions each ofchlorinated biphenyl of 60% chlorination, an extender and propyleneoxide in a volatile solvent onto said selected portions of saidsurfaces, drying each of said plurality of coats before applying asuccessive one of said coats, the ratio of the ingredients of saidcomposition to the unmodified vinyl chloride-vinyl acetate copolymerbeing 1.5 to 4.0 for the modified vinyl chloride-vinyl acetate copolymer0.5 to 2.5 for the chlorinated biphenyl 0.5 to 4.5 for the extender 0.01to 0.9 for the propylene oxide.

9. A method of masking selected portions of surfaces immersed in acidbaths for selective chemical milling, etching, and the like, whichcomprises the steps of applying a plurality of coats of an organicsolvent solution of a non-aqueous composition comprised of a majorportion, by weight, of a blend of an unmodified vinyl chloride-vinylacetate copolymer and vinyl chloride-vinyl acetate copolymer modifiedwith interpolymerized maleic acid, and minor portions each ofchlorinated biphenyl of 60% chlorination, an extender and propyleneoxide in a volatile solvent onto said selected portions of saidsurfaces, the ratio of the ingredients of said composition to theunmodified vinyl chloride-vinyl acetate copolymer being 1.5 to 4.0 forthe modified vinyl chloride-vinyl acetate copolymer 0.5 to 2.5 for thechlorinated biphenyl 0.5 to 4.5 for the extender 0.01 to 0.9 for thepropylene oxide air drying each of said coats for about 20 minutesbefore applying a successive one of said coats, and then air drying saidplurality of coats to produce a film.

10. An organic solvent solution of a non-aqueous coating compositioncapable of drying at room temperature, comprising essentially a Waterimmiscible, unmodified vinyl chloride-vinyl acetate copolymer, a vinylchloridevinyl acetate copolymer modified with about 1% interpolymerizedmaleic acid and further containing chlorinated biphenyl of 60%chlorination and propylene oxide, the ratio of said ingredients to theunmodified vinyl chloride-vinyl acetate copolymer being 1.54.0 for themodified vinyl chloride-vinyl acetate copolymer 0.5-2.5 for thechlorinated biphenyl 0.01 to 0.9 for the propylene oxide.

References Cited in the file of this patent UNITED STATES PATENTS2,498,485 Clawson Feb. 21, 1950 2,516,986 Heinse Aug. 1, 1950 2,520,919Forgie Sept. 5, 1950 2,567,678 Morrison Sept. 11, 1951 2,569,954Rubensaal Oct. 2, 1951 2,626,873 Allen -Q Jan. 27, 1953 2,891,876 BrownJune 23, 1959

8. A METHOD OF MASKING AND IMPEDING THE FLOW OF IONS ONTO AND FROMSELECTED PORTIONS OF SURFACES IMMERSED IN ACID ELECTROPLATING BATHS,ANODIZING BATHS, CHEMICAL ETCHING BATHS AND CHEMICAL MILLING BATHS,WHICH COMPRISES THE STEPS OF APPLYING A PLURALITY OF COATS OF AN ORGANICSOLVENT SOLUTION OF A NON-AQUEOUS COMPOSITION COMPRISED OF A MAJORPORTION, BY WEIGHT, OF A BLEND OF AN UNMODIFIED VINYL CHLORIDE-VINYLACETATE COPOLYMER AND VINYL CHLORIDE-VINYL ACETATE COPOLYMER MODIFIEDWITH INTERPOLYMERIZED MALEIC ACID, AND MINOR PORTIONS EACH OFCHLORINATED BIPHENYL OF 60% CHLORINATION, AN EXTENDER AND PROPYLENEOXIDE IN A VOLATILE SOLVENT ONTO SAID SELECTED PORTIONS OF SAIDSURFACES, DRYING EACH OF SAID PLURALITY OF COATS BEFORE APPLYING ASUCCESSIVE ONE OF SAID COATS, THE RATIO OF THE INGREDIENTS OF SAIDCOMPOSITION TO THE UNMODIFIED VINYL CHLORIDE-VINYL ACETATE COPOLYMERBEING 1.5 TO 4.0 FOR THE MODIFIED VINYL CHLORIDE-VINYL ACETATE COPOLYMER0.5 TO 2.5 FOR THE CHLORINATED BIPHENYL 0.5 TO 4.5 FOR THE EXTENDER 0.01TO 0.9 FOR THE PROPYLENE OXIDE.